I believe that it is more of a personal decision. I like to change my routine up during different parts of the year (which we all should do) and sometimes i change my splits. I have done arms on their own day and the only drawback that i had was sometimes my tri's or bi's were still sore on the chest or back day. Other than that, it is just different

I find that doing , what I call my power exercises, EG: bench hard and then into tri's. EG: heavy one arm rows into bi's helps me to totally exhaust the muscle. Everybody probably has a different way but I tend to get the best pumps when w/o this way.

i like to train my arms all in one day...i use to do chest/tri's, back/bi's but i have changed to one body part per day and i freakin love it b/c i can blast it. but yeah i dont think this is the right froum for this ?...anyways yeah i think it is a personal preference